The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly due to the increased capabilities of computers and increased network speeds and capacity. In order to efficiently receive, distribute, and extract such large volumes of information, storage devices are required that are capable of inputting/outputting large volumes of information at high speed. With magnetic disks, as the recording density is increased, a problem occurs where the recorded signal is progressively attenuated due to thermal fluctuation becoming increasingly acute. The cause of this problem is that the magnetic recording medium consists of magnetic material formed into an assembly of microcrystals, and the volume of these microcrystals is reduced. In order to achieve sufficient stability in regard to thermal fluctuation, it is useful to rely on the commonly-used thermal fluctuation index, Kβ, which equals KuV/kT; where Ku is magnetic anisotropy, V is grain volume, T is absolute temperature, and k is the Boltzmann's constant. Kβ should be at least 70. If it is assumed that Ku and T (material and environment) are fixed, it is seen that magnetization reversal due to thermal fluctuation will tend to increase as the volume, V, of the grains becomes smaller.
As recording densities are increased and the volume of the recording film occupied by one bit is decreased, thermal fluctuation cannot be neglected. If, in order to suppress this thermal fluctuation, Ku is raised, the necessary magnetic field for magnetization reversal in magnetic recording exceeds the recording magnetic field that may be generated by the recording head, so recording becomes impossible.